In recent years, the demand for additives such as flame retardants, antioxidants or UV light absorbers has been increasing with a frequent use of polymer products such as a variety of plastics, synthetic rubbers, nylon fibers or resin coatings. Particularly, in promotion of differentiation of polymer products and making them highly value added, it has become an important problem to use UV light absorbers in order to protect the polymer products against deterioration phenomena due to UV light such as cracks or discoloration, and therefore a stable supply of UV light absorber is required. Representative UV light absorbers include benzophenones, benzotriazoles, cyanoacrylates, salycylates and the like, and they are generally used by kneading into polymer materials as they are, by adding to a coating or an oil, etc. or by preparing an emulsion composition thereof and allowing it to adsorb on fibers. A large number of UV light absorbers known hitherto are excellent in efficiency of UV light absorption, but have problems such as sublimation or volatilization when they are kneaded into polymer materials and heated or processed, or problems that they are gradually volatilized and scattered when the finished products are used. In order to overcome these problems, improvements such as a polymerization of UV light absorbers or an addition of non-volatile functional groups thereto have been attempted, but none was proven to be fully satisfactory. In addition, when UV light absorbers in a polymerized state are handled in a shape of powder, most of them have problems such as dust scattering, low flowability or low shelf stability, and they are required to be improved in powder properties.
It is generally known that 2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolylphenol] is effective as UV light absorbers for plastics, coatings, oil, fibers and the like.
The method of preparation of 2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolylphenol] is disclosed in Japanese Patent Laid-open No. Sho 61-115073 in which 4-(1,1,3,3-tetramethyl)butyl-6-benzotriazol-2-yl phenol is reacted with a dialkylamine and formalin to give a Mannich base, and a reaction crude product obtained upon treating the resulting Mannich base with a base is crystallized from heptane, in Japanese Patent Laid-open No. Hei 4-29087 in which 4-(1,1,3,3-tetramethyl)butyl-6-benzotriazol-2-yl phenol is reacted with a dialkylamine and formalin to give a Mannich base, and a reaction crude product obtained upon treating the resulting Mannich base with a base is crystallized from xylene, or in Japanese Patent Laid-open No. Hei 5-213908 in which 4-(1,1,3,3-tetramethyl)butyl-6-benzotriazol-2-yl phenol and formalin are reacted with concentrated sulfuric acid to give a reaction crude product and the resulting crude product is crystallized from methanol.
However, these patent publications do not describe powder properties such as scattering, flowability or stability on storage of solid-like substances obtained by the method disclosed therein, nor crystalline state of the solid-like substances. Further, only the use of methanol, xylene or heptane as solvent for crystallization is described in examples of the above-mentioned patent publications.
On the other hand, it is generally known that there occurs problems such as dust scattering, low flowability or concretion on storage when the solid-like substances are handled. In order to solve these problems, various investigations are undertaken on crystalline state of the solid-like substances. For example, Japanese Patent Laid-open Nos. Hei 6-128195 and Hei 6-72960 disclose that there are difference in bulk specific gravity, particle size distribution and flowability of powders in each crystal transformation for the same compound. As mentioned above, it is known that even if two compounds belong to the same compound, they are different from each other in functionality or physical properties depending on in what crystal state they are. It is important to obtain such an information for a tendency in order to heighten the added value of products and an improvement in quality thereof. In addition, as practical methods for analyzing substances from the view point of crystal, X-ray diffraction analysis and differential scanning calorimeter analysis are used in various fields such as differentiation of crystal states or development of new functional materials.
2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolylphenol] prepared by the known methods is in a form of fine powder, and causes problems in workability such as scattering or partial agglomerate of the powder during handling including weighing in drying step or packaging step and feeding. Thus, it is desired to provide solid with good flowability which does not affect adversely workability in handling of the powder.
The object of the present invention is to provide a low dusting crystalline 2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolylphenol] type I crystal transformation and a low dusting amorphous 2,2′-methylenebis[4-(1,1,3,3-tetramethylbutyl)-6-benzotriazolylphenol] type II crystal transformation which have excellent UV light absorptive power, exert little sublimation or volatilization, are easy to handle and excellent in workability at use, and cause little dust; methods for preparing these compounds, mixtures containing these compounds and UV light absorbers using these compounds.